This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of various aspects of the present invention. Accordingly, it should be understood that the following statements are to be read in this light, and not as admissions of prior art.
The present invention relates generally to valve actuators. More specifically, the present invention, in accordance with certain embodiments, relates to actuators for subsea or surface high-pressure, large diameter gate valves. As one example, the present invention relates to a combination of a rotary actuator and a high-efficiency mechanical device that converts the rotary motion to linear motion so as to actuate a gate valve.
Increasing performance demands for subsea hydrocarbon production systems have led to a demand for high-performance control systems to operate subsea pressure control equipment, such as valves and chokes. Traditionally, pressure control equipment rely on hydraulic actuators for operation. Hydraulic actuators receive pressurized hydraulic fluid from a direct hydraulic control system or an electrohydraulic control system, for example. Direct hydraulic control systems provide pressurized hydraulic fluid directly from the control panel to the subsea valve actuators. Electrohydraulic control systems utilize electrical signals transmitted to an electrically actuated valve manifold that controls the flow of hydraulic fluid to the hydraulic actuators of the pressure control equipment.
The performance of both direct hydraulic and electrohydraulic control systems is affected by a number of factors, including the water depth in which the components operate, the distance from the facility controlling the operation, and a variety of other constraints. Thus, as water depth and field size increases, the limits of hydraulic control systems, whether hydraulic or electrohydraulic, become an increasing issue. Further, even when the use of a hydraulic control system is technically feasible, the cost of the system may preclude its use in a smaller or marginal field.
In order to provide an alternative to hydraulic control systems, full electrical control systems, including fully electric actuators, have been developed. Instead of relying on pressurized hydraulic fluid to actuate the pressure control components, electrical actuators are supplied with an electric current. The reliance on electric current can allow for improved response times, especially over long distances and/or in deep water.
Thus, there remains a need to develop methods and apparatus for allowing operation of subsea actuators that overcome some of the foregoing difficulties while providing more advantageous overall results.